A032619 Numbers k such that k concatenated with k+4 is a prime.

3, 5, 17, 27, 35, 39, 45, 47, 63, 65, 83, 93, 99, 113, 123, 147, 149, 173, 185, 203, 209, 213, 219, 227, 239, 249, 255, 263, 267, 285, 287, 303, 309, 317, 327, 329, 333, 363, 365, 399, 413, 419, 423, 435, 447, 459, 465, 467, 473, 489, 497, 509, 515, 519

Offset: 1

Author

Patrick De Geest, May 15 1998

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A032609.

Programs

Maple

filter:= n -> isprime(n*(10^(1+ilog10(n+4))+1)+4):
select(filter, [seq(i,i=1..1000,2)]); # Robert Israel, Nov 14 2019

Mathematica

prkk4Q[k_]:=With[{c=k+4},PrimeQ[k*10^IntegerLength[c]+c]]; Select[ Range[ 600],prkk4Q] (* Harvey P. Dale, Aug 31 2021 *)